1. Field of the Invention
This invention pertains to a self expanding stent and delivery system for a self expanding stent. The delivery system allows for reconstraining the stent into the delivery catheter simultaneously allowing the stent to change lengths and rotate inside the delivery catheter if required. This invention also pertains to a delivery system for self expanding stent that foreshortens an appreciable amount, for example more than about 10%.
2. Description of the Related Art
Most commercial self expanding stents are not designed to be recaptured (reconstrained) into the delivery system once the stent has started to expand into the target vessel, artery, duct or body lumen. It would be advantageous for a stent to be able to be recaptured after the stent has started to deploy in the event that the stent is placed in an incorrect or suboptimal location, the stent could be recaptured and redeployed or recaptured and withdrawn. A recapturable stent and delivery system would constitute a major safety advantage over non-recapturable stent and delivery systems.
Many conventional self expanding stents are designed to limit the stent foreshortening to an amount that is not appreciable. Stent foreshortening is a measure of change in length of the stent from the crimped or radial compressed state as when the stent is loaded on or in a delivery catheter to the expanded state. Percent foreshortening is typically defined as the change in stent length between the delivery catheter loaded condition (crimped) and the deployed diameter up to the maximum labeled diameter divided by the length of the stent in the delivery catheter loaded condition (crimped). Stents that foreshorten an appreciable amount are subject to more difficulties when being deployed in a body lumen or cavity, such as a vessel, artery, vein, or duct. The distal end of the stent has a tendency to move in a proximal direction as the stent is being deployed in the body lumen or cavity. Foreshortening may lead to a stent being placed in an incorrect or suboptimal location. Delivery systems that can compensate for stent foreshortening would have many advantages over delivery systems that do not.
A stent is a tubular structure that, in a radially compressed or crimped state, can be inserted into a confined space in a living body, such as a duct, an artery or other vessel. After insertion, the stent can be expanded radially at the target location. Stents are typically characterized as balloon-expanding (BX) or self-expanding (SX). A balloon-expanding stent requires a balloon, which is usually part of a delivery system, to expand the stent from within and to dilate the vessel. A self expanding stent is designed, through choice of material, geometry, or manufacturing techniques, to expand from the crimped state to an expanded state once it is released into the intended vessel. In certain situations higher forces than the expanding force of the self expanding stent are required to dilate a diseased vessel. In this case, a balloon or similar device might be employed to aid the expansion of a self expanding stent.
Stents are typically used in the treatment of vascular and non-vascular diseases. For instance, a crimped stent may be inserted into a clogged artery and then expanded to restore blood flow in the artery. Prior to release, the stent would typically be retained in its crimped state within a catheter and the like. Upon completion of the procedure, the stent is left inside the patient's artery in its expanded state. The health, and sometimes the life, of the patient depend upon the stent's ability to remain in its expanded state.
Many conventional stents are flexible in their crimped state in order to facilitate the delivery of the stent, for example within an artery. Few are flexible after being deployed and expanded. Yet, after deployment, in certain applications, a stent may be subjected to substantial flexing or bending, axial compressions and repeated displacements at points along its length, for example, when stenting the superficial femoral artery. This can produce severe strain and fatigue, resulting in failure of the stent.
A similar problem exists with respect to stent-like structures. An example would be a stent-like structure used with other components in a catheter-based valve delivery system. Such a stent-like structure holds a valve which is placed in a vessel.